Method and system for handling the transcoding of connections handed off between mobile switching centers

ABSTRACT

A communication system supports multiple source coding and/or channel coding schemes. When a handoff is needed that transfers radiocommunication service support responsibility from a base station controlled by one MSC to a base station controlled by another MSC, signaling procedures are employed to handle the transfer as it pertains to the source coding and/or channel coding, i.e., ensuring that the new MSC links in an appropriate codec to support the handed off connection. Various techniques are described to provide such signaling, both in the direction of the new (target) MSC and in the direction of the user equipment being handed off.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.09/742,396 filed on Dec. 22, 2000 now U.S. Pat. No. 6,810,256, whichclaims the benefit under 35 U.S.C. Section 119(e) of U.S. applicationSer. No. 60/174,165 filed on Jan. 3, 2000, the disclosures of which areincorporated herein by reference.

BACKGROUND

The present invention generally relates to coding in the field ofcommunication systems and, more particularly, to handling the signalingfor controlling transcoding when a connection is handed off betweenmobile switching centers (MSCs) in radiocommunication systems.

The growth of commercial communication systems and, in particular, theexplosive growth of cellular radiotelephone systems, have compelledsystem designers to search for ways to increase system capacity withoutreducing communication quality beyond consumer tolerance thresholds. Onetechnique to achieve these objectives involved changing from systemswherein analog modulation was used to impress data onto a carrier wave,to systems wherein digital modulation was used to impress the data oncarrier waves.

In wireless digital communication systems, standardized air interfacesspecify most of the system parameters, including speech coding type(s),burst format, communication protocol, etc. For example, the EuropeanTelecommunication Standard Institute (ETSI) has specified a GlobalSystem for Mobile Communications (GSM) standard that uses time divisionmultiple access (TDMA) to communicate control, voice and datainformation over radio frequency (RF) physical channels or links using aGaussian Minimum Shift Keying (GMSK) modulation scheme at a symbol rateof 271 ksps. In the U.S., the Telecommunication Industry Association(TIA) has published a number of Interim Standards, such as IS-54 andIS-136, that define various versions of digital advanced mobile phoneservice (D-AMPS), a TDMA system that uses a differential quadraturephase shift keying (DQPSK) modulation scheme for communicating data overRF links.

TDMA systems subdivide the available frequency into one or more RFchannels. The RF channels are further divided into a number of physicalchannels corresponding to time slots in TDMA frames. Logical channelsare formed of one or several physical channels where modulation andcoding is specified. In these systems, the mobile stations communicatewith a plurality of scattered base stations by transmitting andreceiving bursts of digital information over uplink and downlink RFchannels.

The growing number of mobile stations in use today has generated theneed for more voice and data channels within cellular telecommunicationsystems. As a result, base stations have become more closely spaced,with an increase in interference between mobile stations operating onthe same frequency in neighboring or closely spaced cells. In fact, somesystems now employ code division multiple access (CDMA), using a form ofspread spectrum modulation wherein signals intentionally share the sametime and frequency. Although digital techniques provide a greater numberof useful channels from a given frequency spectrum, there still remainsa need to maintain interference at acceptable levels, or morespecifically to monitor and control the ratio of the carrier signalstrength to interference, (i.e., carrier-to-interference (C/I) ratio).

Another factor which is increasingly important in providing variouscommunication services is the desired/required user bit rate for data tobe transmitted over a particular connection. For example, for voiceand/or data services, user bit rate corresponds to voice quality and/ordata throughput, with a higher user bit rate producing better voicequality and/or higher data throughput. The total user bit rate isdetermined by a selected combination of techniques for speech coding,channel coding, modulation, and resource allocation, e.g., for a TDMAsystem, this latter technique may refer to the number of assignable timeslots per connection, for a CDMA system, this latter parameter may referto the number of assignable codes per connection.

Speech coding (or more generally “source coding”) techniques are used tocompress the input information into a format which uses an acceptableamount of bandwidth but from which an intelligible output signal can bereproduced. Many different types of speech coding algorithms exist,e.g., residual excited linear predictive (RELP), regular-pulseexcitation (RPE), etc., the details of which are not particularlyrelevant to this invention. More significant in this context is the factthat various speech coders have various output bit rates and that, asone would expect, speech coders having a higher output bit rate tend toprovide greater consumer acceptance of their reproduced voice qualitythan those having a lower output bit rate. As an example, consider thatmore traditional, wire-based telephone systems use PCM speech coding at64 kbps, while GSM systems employ an RPE speech coding scheme operatingat 13 kbps.

In addition to speech coding, digital communication systems also employvarious techniques to handle erroneously received information. Generallyspeaking, these techniques include those which aid a receiver to correctthe erroneously received information, e.g., forward error correction(FEC) techniques, and those which enable the erroneously receivedinformation to be retransmitted to the receiver, e.g., automaticretransmission request (ARQ) techniques. FEC techniques include, forexample, convolutional or block coding (collectively referred to hereinas “channel coding”) of the data prior to modulation. Channel codinginvolves representing a certain number of data bits using a certainnumber of code bits. Thus, for example, it is common to refer toconvolutional codes by their code rates, e.g., ½ and ⅓, wherein thelower code rates provide greater error protection but lower user bitrates for a given channel bit rate.

Conventionally, each of the techniques which impacted the user bit ratewere fixed for any given radiocommunication system, or at least for theduration of a connection established by a radiocommunication system.That is, each system established connections that operated with one typeof speech coding, one type of channel coding, one type of modulation andone resource allocation. More recently, however, dynamic adaptation ofthese techniques has become a popular method for optimizing systemperformance in the face of the numerous parameters which may varyrapidly over time, e.g., the radio propagation characteristics ofradiocommunication channels, the loading of the system, the user's bitrate requirements, etc. This type of dynamic adaptation of codingtechniques has been referred to in the GSM standard as adaptivemultirate (AMR) communications. AMR techniques and the like are likelyto be used in next generation radiocommunication systems, e.g.,Universal Mobile Telecommunication Systems (UMTS).

In GSM systems, AMR techniques have been traditionally been coordinatedby the base station controller (BSC). For context, consider FIG. 1,which depicts various nodes in a hybrid UMTS/GSM communication system10. This Figure will also be referred to below in describing aspects ofthe present invention. The system 10 is designed as a hierarchicalnetwork with multiple levels for managing calls. Using a set of uplinkand downlink frequencies, mobile stations 12 operating within the system10 participate in calls using time slots allocated to them on thesefrequencies. At an upper hierarchical level, a group of Mobile SwitchingCenters (MSCs) 14 a-14 c are responsible for the routing of calls froman originator to a destination. In particular, these entities areresponsible for setup, control and termination of calls. One of the MSCs14 a, known as the gateway MSC, handles communication with a PublicSwitched Telephone Network (PSTN) 18, or other public and privatenetworks.

At a lower hierarchical level, each of the MSCs 14 a-14 c are connectedto a group of BSCs 16 a-b (although the BSCs are only depicted for MSC14 b to simplify the figure) using, for example, PCM (pulse codemodulated) links. Under the GSM standard, the BSCs 16 a-16 b communicatewith MSCs 14 a-14 c under a standard interface known as the A-interface,which is based on the Mobile Application Part (MAP) of CCITT SignalingSystem No. 7. Under the UMTS standard, the BSCs are referred to as radionetwork controllers (RNCs) and communicate with the MSCs 14 a-14 c overa standard interface known as the Iu interface.

At a still lower hierarchical level, each of the BSCs (RNCs) 16 controlsa group of base transceiver stations (BTSs) 20. Each BTS 20 includes anumber of TRXs (not shown) that use the uplink and downlink RF channelsto serve a particular common geographical area, such as one or morecommunication cells 21. The BTSs 20 primarily provide the RF links forthe transmission and reception of data bursts to and from the mobilestations 12 within their designated cell. As mentioned earlier, theinformation transmitted on these RF links may be speech coded in variousways to enhance various aspects of communication over the air interface,which coding is controlled in conventional GSM systems by theresponsible BSC.

However, in next generation systems (e.g., UMTS) it has been proposedthat the coding of this information be controlled by the MSC rather thanthe radio network controller (RNC), which is the nomenclature for thenode corresponding to the BSC in third generation systems. This shiftingof responsibility leads to a number of problems regarding management ofcoding, particularly during handoffs of connections between MSCs. Forexample, it will be necessary to know which MSC, i.e., the serving(anchor) MSC or the target MSC, will control the transcoder.Additionally, it will be useful to define where the radio access networkprotocol is terminated and the format for signaling between the MSCsinvolved in the handoff to control coding parameters.

Accordingly, it will be desirable to provide methods and systems forhandling the transcoding of connections being handed off between MSCswhich take into account these various aspects of emerging, nextgeneration communication systems.

SUMMARY

These and other drawbacks, problems and limitations of conventionalradiocommunication systems are overcome according to the presentinvention, wherein various signaling techniques and protocols aredescribed for handling codec issues during inter-MSC handoff. Forexample, exemplary embodiments of the present invention handle codecissues associated with inter-MSC handoff by determining at least onecodec that is available in a target MSC, selecting, by an anchor MSC,one of the available codecs for handling the connection, signaling thetarget MSC with an indication of the selected codec, and informing theuser equipment of the selected codec.

Various exemplary embodiments perform these signaling steps in differentways. For example, the determination of available codecs in the targetMSC may (or may not) require signaling to ascertain the target MSC'scodec capabilities. If such signaling is performed, mobile applicationpart (MAP) protocol messages may be used.

According to another aspect of the present invention, the signaling usedto inform the target MSC of the selected codec may take any of aplurality of different forms. For example, the selected codecinformation may be forwarded to the target MSC as a MAP message which isindependent of another message wherein the radio access bearer (RAB)assignment is forwarded. Alternatively, the selected codec informationcan be passed to the target MSC using the same message by which the RABis assigned. Different protocols, e.g., radio access network applicationprotocol (RANAP) or base station system management application part(BSSMAP) can be used to as the signaling protocol for these messages.

Likewise, signals informing the user's equipment of the selected codeccan be provided in different forms. For example, a call control messagecan be sent to the user's equipment identifying the selected codec sothat it is prepared to properly process messages for transmission andreception after the inter-MSC handoff. Alternatively, an RANAP messageidentifying the RAB can also be used to convey selected codecinformation to the user equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become more apparent upon reading from the followingdetailed description, taken in conjunction with the accompanyingdrawings, wherein:

FIG. 1 is a block diagram of an exemplary GSM communication system whichadvantageously uses the present invention;

FIG. 2 is a flow chart depicting a general set of steps for handlinginter-MSC handoff according to exemplary embodiments of the presentinvention;

FIG. 3 is a signaling/block diagram which depicts inter-MSC handoffsignaling according to an exemplary embodiment. of the presentinvention;

FIG. 4 is a signaling/block diagram which depicts inter-MSC handoffsignaling according to another exemplary embodiment of the presentinvention;

FIG. 5 is a signaling/block diagram which depicts inter-MSC handoffsignaling according to yet another exemplary embodiment of the presentinvention;

FIGS. 6( a) and 6(b) depict protocol stacks for the control plane anduser plane, respectively, for the exemplary embodiments of FIG. 5;

FIG. 7 is a signaling/block diagram which depicts inter-MSC handoffsignaling according to still another exemplary embodiment of the presentinvention;

FIGS. 8( a) and 8(b) depict protocol stacks for the control plane anduser plane, respectively, for the exemplary embodiment of FIG. 7; and

FIG. 9 is a signaling/block diagram which depicts inter-MSC handoffsignaling according to still another exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION

The various features of the invention will now be described withreference to the figures, in which like parts are identified with thesame reference characters. In the following description, for purposes ofexplanation and not limitation, specific details are set forth, such asparticular circuits, circuit components, techniques, etc. in order toprovide a thorough understanding of the present invention. However, itwill be apparent to one skilled in the art that the present invention.may be practiced in other embodiments that depart from these specificdetails. In other instances, detailed descriptions of well-knownmethods, devices, and circuits are omitted so as not to obscure thedescription of the present invention.

The following exemplary embodiments are provided in the context of TDMAradiocommunication systems. However, those skilled in the art willappreciate that this access methodology is merely used for the purposesof illustration and that the present invention is readily applicable toall types of access methodologies including frequency division multipleaccess (FDMA), TDMA, code division multiple access (CDMA) and hybridsthereof.

Moreover, operation in accordance with GSM communication systems isdescribed in, for example, European Telecommunication Standard Institute(ETSI) documents ETS 300 573, ETS 300 574 and ETS 300 578, which arehereby incorporated by reference. Therefore, the operation of the GSMsystem is only described herein to the extent necessary forunderstanding the present invention. Similar standards related documentsare also available for UMTS. Although, the present invention isdescribed in terms of exemplary embodiments in a UMTS/GSM system, thoseskilled in the art will appreciate that the present invention may beapplicable to digital communication systems.

When user equipment (UE), e.g., a mobile phone or personal digitalassistant, moves to a location wherein its wireless connection with afixed network has deteriorated to a point where a new connection isdesirable, a handoff procedure is initiated to provide the UE withcontinued service via a different portion of the fixed network. In somecases, the best candidate base station for providing this continuedservice is controlled by a different (target) MSC than that which iscurrently controlling the UE's service, i.e., the anchor MSC, in whichcase the handoff can be referred to as an “inter-MSC” handoff. Variouscontrol signaling is performed in order to accomplish inter-MSChandoffs.

In general, the handling of codec control during inter-MSC handoffaccording to the present invention follows a number of steps asillustrated in FIG. 2. Therein, at step 100, the codecs available in thetarget MSC are determined. Those skilled in the art will appreciate thatnot all MSCs will contain the same type and number of codecs and,therefore, it is useful to determine the target MSCs codec capabilitiesbefore making a codec selection. This determination may be ratherstraightforward if the codecs supported by the target MSC areadministered by the anchor MSC. Alternatively, a message can betransmitted from the anchor MSC to the target MSC to request a supportedcodec list therefrom. These messages may be formatted as, for example,MAP messages since MAP messages will terminate in the target MSC.

In any event, once the anchor MSC has determined the codecs available inthe target MSC, a codec selection is made to determine which codec inthe target MSC shall be linked in to handle the connection once it hasbeen handed off (step 102). This selection can be based on a comparisonbetween the codec list associated with the target MSC and the codecssupported by the UE, the latter of which can be identified to the anchorMSC during call set-up. For example, the call setup message (or callconfirmation message) transmitted from the UE to the anchor MSC mayinclude a GSM codec list and a UMTS codec list. Separate lists may beprovided for each system in order to ensure unique codec identification,e.g., since AMR for GSM and AMR for UMTS may differ in rate adaptationand discontinuous transmission (DTX) modes. Additionally, the UE maytransmit a separate intersystem code handoff list which may includepreferences for the codec selected during inter-MSC handoff describedbelow. If the target MSC and the UE support more than one of the samecodecs, then a selection from among the common codecs can be made basedon preferences, e.g., either network preferences, UE preferences or somecombination thereof. The particular mechanism by which a particularcodec is selected for handling the connection after the handoff isbeyond the scope of this discussion.

After a codec is selected for use in the target MSC, the target MSCneeds to be informed of that selection in step 104 so that it can linkin the selected codec to handle the connection once it is handed off.Likewise, at step 106, the UE needs to be informed of the codecselection so that it can employ the appropriate codec post-handoff.Those skilled in the art will appreciate that steps 104 and 106 can beperformed in any temporal order including simultaneously.

Those skilled in the art will also appreciate that steps 100-106illustrated in FIG. 2 can be implemented in many different waysdepending, for example, upon network topologies and which systems, e.g.,GSM and/or UMTS, are involved in the inter-MSC handoff process. Severalexamples will now be provided to illustrate these variations.

Consider the example of FIG. 3 for a handoff between two MSCs whichoperate in accordance with the UMTS standard. Therein, a UE 300 needs ahandoff (relocation required by RNC) due to, for example, a change inposition relative to a serving RNC 302 or base station (not shown)associated therewith. A relocation request is communicated through tothe anchor MSC 304 which then begins, among other tasks, to coordinatethe codec transition to the new (target) MSC 306. In this particularexample, the anchor MSC 304 administers the codecs in the target MSC306, such that no signaling needs to be performed between the two MSCsto establish the codec capability of the target MSC 306 prior to aselection being made. The anchor MSC 304 can, therefore, make its codecselection based upon its a priori knowledge of the codecs available inthe target MSC 306, UE 300 and preferences.

Once a codec selection is made, the anchor MSC 304 informs the targetMSC 306 and UE 300 of the selection using different mechanisms.According to this exemplary embodiment, the anchor MSC 304 sends aBSSMAP Prepare HandoverRequest Message which includes, as a parameter,the preferred speech version over a synchronous transfer mode (STM) link308. The preferred speech version indicates which type of codec is to beseized by the target MSC 306 for this handoff. Those skilled in the artwill recognize that BSSMAP is the acronym for Base Station SystemManagement Application Part which identifies a protocol which is usedover the A-interface. Those interested readers desiring more informationregarding BSSMAP protocols are directed to the published standard GSM08.08: “Digital cellular telecommunications system (Phase 2+); MobileSwitching Centre—Base Station System (MSC-BSS) interface Layer 3specification,” the disclosure of which is incorporated here byreference, for more information. The BSSMAP message may also inform thetarget MSC 306 which radio access bearer (RAB) is requested for the newconnection. The target MSC 306, in turn, provides the relevant RNC 310with a Relocation Request over the Iu interface to alert it to itsresponsibilities for the handoff of UE 300 thereto. The target MSC 306also acknowledges the PrepareHandover Request message to the anchor MSC304. In the UE direction, the anchor MS 304 sends a call control (CC)message informing the UE 300 of the selected codec.

According to another embodiment of the present invention illustrated inFIG. 4, the inter-MSC handoff occurs from a UMTS network to a GSMnetwork. Therein, similar reference numerals are used to refer tosimilar functional units as set forth above with respect to FIG. 3.Morever, to avoid redundancy, those similarities between the twoembodiments are not repeated here and reference is made to the foregoingfor the description of similar signaling. Unlike the embodiment of FIG.3, however, the target MSC 306 coordinates with a target BSC 400 whichcontains the transcoder unit (TRAU) to be used to support the UE 300after the handoff. Thus, in this embodiment, the selected codecinformation is passed from the target MSC 306 to the BSC 400 over theA-interface via a Handover Request message. Also note that the link 308between the (GSM) target MSC 306 and the (UMTS) anchor MSC 304 caneither be an STM link or an asynchronous transfer mode (ATM) link.

Another variation of a UMTS MSC to UMTS MSC handoff is depicted in theexemplary embodiment of FIG. 5. Again, similar reference numerals areused to refer to similar functional units as set forth above withrespect to FIG. 3 and differences are discussed with respect thereto.Therein, the anchor MSC 304 is not responsible for administering thecodecs supported by the target MSC 306. Accordingly, step 100 of FIG. 2is performed by sending a MAP message requesting that the supportedcodecs be identified over the STM link 308 and receiving a MAP responseindicating those supported codecs so that the anchor MSC 304 can thenselect a codec, e.g., by comparison to a list supplied by UE 300 andpreferences, for the handoff.

Once a codec is selected, the anchor MSC 304 sends a MAP messageindicating the selected codec to the target MSC 306. Unlike theembodiment of FIG. 3, the signaling associated with the selected codecin this embodiment is separate from the signaling relocation requestsignaling, which permits the relocation request signaling to be codecindependent. This, in turn, provides for a clear separation offunctionality as MAP signaling is used in both GSM and UMTS systems andterminates in the target MSC. Additionally, the embodiment of FIG. 5employs the RANAP protocol for transmitting the relocation requestmessage, as opposed to the BSSMAP protocol employed in the exemplaryembodiment of FIG. 3. Those skilled in the art will recognize that RANAPis the acronym for Radio Access Network Application Protocol whichidentifies the protocol defined for use over the Iu interface betweenUMTS MSCs and RNCs to maintain links there between. For more informationregarding RANAP signaling in general, the interested reader is directedto the published standard 3GPP 25.413: “Iu interface RANAP signaling,”the disclosure of which is incorporated here by reference.

The embodiments of FIGS. 3-5 are depicted using signaling diagrams andfunctional block units. However, as will be appreciated by those skilledin the art, the choice of signaling protocols used to perform codechandling during inter-MSC handoff according to the present invention canalso be described using protocol stacks. The resulting protocol stacksafter handoff from the anchor MSC 304 to the target MSC 306 (with an STMlink there between) are illustrated in FIGS. 6( a) and 6(b) for thecontrol plane and user plane, respectively. A non-access stratum (NAS)container can be used to covey the chosen codec information from the MSCto the UE.

If ATM links are used between the MSCs involved in the handoff, then ATMneed not be terminated in the target MSC 306 and compressed speech, forexample, can be passed transparently through the target MSC 306 to theanchor MSC 304. This means, in turn, that transcoding need notnecessarily be performed in the target MSC 306 and, instead, can beperformed in the anchor MSC 304. One exemplary embodiment whichillustrates an inter-MSC handoff using an ATM link is provided as FIG.7. Therein, it will be noted that the signaling used to perform theinter-MSC handoff is similar as that described above and illustrated inFIG. 5, with the exception that there is no need to inform the targetMSC 306 of the selected codec, since the same codec in the anchor MSC304 is used both pre- and post-handoff. Thus, from the protocol stackperspective (see FIGS. 8( a) and 8(b)), the target MSC 306 istransparent on the user plane and is used only for performing RANAPcontrol signaling. Those skilled in the art will appreciate thatalthough the embodiment of FIGS. 7, 8(a) and 8(b) provides certainadvantages, e.g., compressed speech through to anchor MSC and continueduse of the same codec after handoff, that the techniques described abovewith respect to FIGS. 3-5 can also be used in circumstances where ATMlinks exist between the relevant MSCs.

FIG. 9 depicts yet another example of signaling between various unitsassociated with inter-MSC handoff according to the present invention.Therein, the UE 300's codec lists are forwarded to the system duringcall setup. The target MSC is interrogated via MAP signaling for itslist of supported/available codecs, after which the anchor selects acodec for the handoff. The UE and the target MSC are informed of theselection via various MAP and/or RANAP signaling as shown.

Although the invention has been described in detail with reference onlyto a few exemplary embodiments, those skilled in the art will appreciatethat various modifications can be made without departing from theinvention. Accordingly, the invention is defined only by the followingclaims which are intended to embrace all equivalents thereof.

1. A method for providing radio communications with a user equipmentwithin a mobile communications network, comprising the steps of:determining to handover a connection associated with said user equipmentfrom an anchor mobile switching center (MSC) to a target MSC;determining at least one codec that is available in said target MSC bysaid anchor MSC; storing said at least one codecs for said target MSCwithin said anchor MSC; selecting, by said anchor MSC, one of said atleast one available codecs for handling said connection; signaling saidtarget MSC with an indication of said selected one of said at least oneavailable codecs; informing said user equipment of said selected one ofsaid at least one available codecs by said anchor MSC; receiving, atsaid anchor MSC from said user equipment, an indication of at least onecodec supported by said user equipment; wherein separate lists ofavailable codecs are received from said user equipment for differenttypes of accesses.
 2. The method of claim 1, wherein said step ofsignaling said target MSC further comprises the step of: transmitting amobile application part (MAP) message which includes said indication ofsaid selected one of said at least one available codec to said targetMSC from said anchor MSC.
 3. The method of claim 1, further comprisingthe step of: transmitting a mobile application part (MAP) message whichincludes said indication of said selected one of said at least oneavailable codec to said target MSC from said anchor MSC; andtransmitting, as a message which is independent of said MAP message, aradio access bearer (RAB) assignment message from said anchor MSC tosaid target MSC.
 4. The method of claim 3, wherein step of signalingsaid target MSC further comprises the step of: transmitting a radioaccess network application protocol (RANAP) message which includes saidindication of said selected one of said at least one available codec tosaid target MSC from said anchor MSC.
 5. The method of claim 4, furthercomprising the step of: terminating said RANAP message in said anchorMSC and forwarding said indication to said user equipment as part ofsetup message.
 6. The method of claim 3, wherein said step of signalingsaid target MSC further comprises the step of: transmitting a basestation system management application part (BSSMAP) message whichincludes said indication of said selected one of said at least oneavailable codec to said target MSC from said anchor MSC.
 7. The methodof claim 1, wherein said step of informing said user equipment furthercomprises the step of: forwarding an indication of said selected one ofsaid at least one available codecs to said user equipment as part of aradio access network application protocol (RANAP) message which includesa radio access bearer (RAB) assignment.
 8. A mobile switching center forproviding radio communications with a user equipment within a mobilecommunications network, comprising: means for determining to handover aconnection associated with said user equipment from an anchor mobileswitching center (MSC) to a target MSC; means for determining at leastone codec that is available in said target MSC by said anchor MSC; meansfor storing said at least one codecs for said target MSC within saidanchor MSC; means for selecting, by said anchor MSC, one of said atleast one available codecs for handling said connection; means forsignaling said target MSC with an indication of said selected one ofsaid at least one available codecs; means for informing said userequipment of said selected one of said at least one available codecs bysaid anchor MSC: means for transmitting a mobile application part (MAP)message which includes said indication of said selected one of said atleast one available codec to said target MSC from said anchor MSC; andmeans for transmitting, as a message which is independent of said MAPmessage, a radio access bearer (RAB) assignment message from said anchorMSC to said target MSC.
 9. The mobile switching center of claim 8,further comprises: means for transmitting, as a message which isindependent of said MAP message, a radio access bearer (RAB) assignmentmessage from said anchor MSC to said target MSC; and means fortransmitting a radio access network application protocol (RANAP) messagewhich includes said indication of said selected one of said at least oneavailable codec to said target MSC from said anchor MSC.
 10. The mobileswitching center of claim 9, further comprises: means for transmitting abase station system management application part (BSSMAP) message whichincludes said indication of said selected one of said at least oneavailable codec to said target MSC from said anchor MSC.
 11. The mobileswitching center of claim 8, further comprises: means for forwarding anindication of said selected one of said at least one available codecs tosaid user equipment as part of a radio access network applicationprotocol (RANAP) message which includes a radio access bearer (RAB)assignment.